1. Field of the Invention
The present invention relates to a method for manufacturing an SOI (silicon on insulator) substrate and a method for manufacturing a semiconductor device using the SOI substrate.
2. Description of the Related Art
In recent years, an integrated circuit using an SOI (silicon on insulator) substrate in which a thin single crystal semiconductor layer is provided on an insulating surface, instead of a bulk silicon wafer has been researched. An SOI substrate enables parasitic capacitance formed by a drain of a transistor and a substrate to be small, and therefore an SOI substrate has greatly attracted attention as an element for improving performance of semiconductor integrated circuits.
The Smart Cut (registered trademark) method is known as one of methods for manufacturing an SOI substrate (for example, see Patent Document 1). An outline of the method for manufacturing an SOI substrate by the Smart Cut (registered trademark) method is described below. First, hydrogen ions are implanted into a silicon wafer by an ion implantation method to form a microbubble layer at a predetermined depth from the surface. Then, the silicon wafer into which the hydrogen ions are implanted is bonded to another silicon wafer with a silicon oxide film interposed therebetween. After that, thermal treatment is performed, so that a thin film of the silicon wafer into which the hydrogen ions are implanted is separated at the microbubble layer. Accordingly, a single crystal silicon film is formed over the other bonded silicon wafer. Smart Cut (registered trademark) method may be referred to as a hydrogen ion implantation separation method.
A method has also been proposed in which a single crystal silicon layer is formed over a base substrate made of glass by such Smart Cut (registered trademark) method (for example, see Patent Document 2). Glass substrates, the areas of which can be increased more easily than silicon wafers and which are less expensive than silicon wafers, are mainly used for manufacturing liquid crystal display devices and the like. With the use of glass substrates as base substrates, inexpensive large-area SOI substrates can be manufactured.